Embodiments of the invention relate generally to electrical machines and, more particularly, to permanent magnet electrical machines that include ferrite permanent magnets, with the stator and/or rotor in the electrical machine being heated in order to prevent demagnetization of the ferrite permanent magnets.
The usage of electrical machines in various industries has continued to become more prevalent in numerous industrial, commercial, and transportation industries over time. In an attempt to realize high performance in electric machines, the choice of using permanent magnet (PM) materials is getting more and more popular for many applications. In such machines, the PMs can either replace electromagnets in traditional designs, or novel topologies can be developed to make the best use of the properties and characteristics of PMs.
One PM electrical machine topology that has been developed is referred to as “stator permanent magnet machines,” which are electrical machines that are designed such that the PMs in the machine are positioned on the stator. Stator permanent magnet machines can thus refer to, but are not limited to, permanent magnet flux switching machines, permanent magnet flux reversal machines, and doubly-salient permanent magnet machines. Another PM electrical machine topology that has been developed is referred to as “internal permanent magnet (IPM) machines,” which are electrical machines that are designed such that the PMs in the machine are embedded inside multiple laminations of a rotor. IPM machines can thus refer to IPM motors or generators widely used in a variety of applications, including aircraft, automobiles and industrial usage.
One issue that is taken into consideration when constructing and operating a PM electrical machine is demagnetization of the PMs. Depending on the type of PMs employed, demagnetization of the PMs can occur if the electrical machine is exposed to extremely high or extremely low temperatures. For example, if the PMs are rare earth magnets, exposure of the PMs to extremely high temperatures can make the PMs more susceptible to demagnetization. Conversely, if the PMs are ferrite magnets, exposure of the PMs to low temperatures (e.g., −40° to 60° C.) can make the PMs more susceptible to demagnetization.
It is recognized that the use of ferrite magnets in PM electrical machines can provide cost savings as compared to the use of rare earth magnets, and thus the use of ferrite magnets may be desirable in such PM electrical machines. While ferrite magnets are more prone to demagenetization at lower temperatures compared to rare earth magnets, they are less prone to demagnetization at higher temperatures than rare earth magnets. Thus, if solutions can be provided for preventing demagnetization of ferrite magnets at low temperatures, ferrite magnet PM machines can be a desirable alternative to rare earth magnet PM machines.
Therefore, it is desirable to provide a system and method for preventing the demagnetization of ferrite magnets in a PM machine. It is further desirable to provide a ferrite magnet PM machine useable over a wide range of ambient temperatures and that exhibits improved resistance to corrosion and improved stability.